Wireless communication is ubiquitous and deployments are growing rapidly. In 2014 the International Telecommunication Union projects that the number of mobile telephones will exceed 7.3 billion, up from 4.1 billion in 2008, with a worldwide population of approximately 7.1 billion people. By 2017, global mobile Internet users expected to send and receive approximately 10 Exabytes of mobile data each month, up from the approximately 1.6 Exabytes per month projected in 2014. Over this timeframe the average mobile network connection speed will increase from approximately 1 Mbps to approximately 4 Mbps (see for example “Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update, 2012-2017”, February 2013). However, over the same time frame the total number of devices connected to the Internet will have grown to over 30 billion, reaching approximately 50 billion in 2020. With low cost wireless transceivers a significant portion of these will be wireless devices.
By contrast the wireless spectrum is a scarce and limited resource allocated in to many different communications and RF applications with only a few small segments for the many different communication uses associated with wireless devices by consumers and business users (see for example www.ntia.doc.gov/osmhome/allochrt.pdf). The 2008 spectrum auction in the US provides a good indication of spectrum scarcity and resulting value. The Federal Communications Commission (FCC) auctioned a relatively tiny 62 MHz segment of spectrum across the United States for a total of US$19.6B (http://wireless.fcc.gov/auctions/default.htm?job=auction_summary&id=73). Similar auctions in Germany, United Kingdom and Netherlands for a variety of 2×5 MHz, 2×10 MHz, and 2×20 MHz spectral slices at 800/900/1800/1900 MHz raising $3.6 billion, $5.1 billion, $4.7 billion. Such auctions have established average pricing of approximately $750 million/MHz in currently mature congested spectral region of 800 MHz for Long Term Evolution (LTE), and approximately $350 million/MHz and $100 million in the less mature/less deployed LTE spectral regions of 1800 MHz and 2600 MHz.
To satisfy the increasing demands for performance and throughput, wireless physical layer designs are becoming increasingly complex. In the nearly thirty years of commercial wireless networks have evolved from frequency division multiple access (FDMA, so-called 1G), through time division multiple access (TDMA, so-called 2G) for Global System for Mobile Communications (GSM) systems in the 1990s followed by code division multiple access (CDMA, so-called 3G) in the early 2000s. Today, so-called fourth-generation (4G) LTE and WiMAX and next generation wireless local area network (LAN) IEEE 802.11n systems exploit Multiple-Input-Multiple-Output (MIMO) antennae, orthogonal frequency division multiple access (OFDMA), frequency hopping, complex modulation and packet-based transmission formats and advanced error correction. These wireless systems are complex to deploy, operate, maintain and monitor to support a wide variety of delay-sensitive and delay-insensitive traffic including voice, data, streaming audio, and streaming video.
Wireless communications are sensitive to, and increasingly subjected to, radio interference. As the density of wireless devices increases and the supported datarates increase so does the density of wireless base stations and bandwidth per user. Simultaneously corporations, municipalities, individuals are increasingly deploying or expanding wireless networks for a wide variety of applications from security applications, personal-local area networks (PANs/LANs), equipment communications and control, etc. Wireless 802.11 LANs occupy the same spectrum as Bluetooth, cordless phones and microwave ovens and “must accept any interference” (en.wikipedia.org/wiki/ISM_band). In addition to these sources of unintentional interference there is the issue of RF devices transmitting with malicious intent and the requirement in some environments for real-time radio jamming of transmitter signals.
The rapid growth of deployments, scarcity of spectrum, complexity of solutions, congestion and interference are increasingly compounded problems for those deploying, managing, maintaining and monitoring wireless services. The wireless spectrum is a shared resource where globally national governments not only license the use of the spectrum but must also police that spectrum. Policing ensures that those who are not authorized are not transmitting and those who have spent hundreds or thousands of millions of dollars licensing portions of the spectrum have unencumbered access to those portions. Specifically, government agencies monitor the wireless spectrum within their countries to determine the occupancy within specific segments of the spectrum, to enforce allocation, to police issues pertaining to interference, and for a variety of other legal and strategic objectives. Consequently this results in either the requirement to maintain and deploy expensive personnel and equipment to continually or periodically monitor wireless activity within a network or environment or a decision to not monitor and police the wireless spectrum. Accordingly it would be beneficial for a wide bandwidth, real-time spectrum analyzer to be provided supporting applications across geographically distributed and localized networks allowing enforcement and monitoring of regulated, sensitive, and/or problematic wireless environments. FIG. 1A depicts the 300 MHz-3 GHz region of wireless spectrum in the continental US as licensed by the FCC showing the large number of small frequency band licensed, e.g. 2345 MHz-2360 MHz, and in many instance multiple licensed uses for such a frequency band, e.g. radiolocation, mobile, fixed, broadcast satellite, and amateur.
In many frequency bands characteristics of transmitters, e.g. power, center frequency, 1 dB bandwidth, roll-off rate, etc. may be unregulated within a 100 MHz band, e.g. Industrial, Scientific and Medical band 2450±50 MHz, whereas in others, e.g. GSM 900 MHz band 124 channels are defined upon a 200 kHz frequency grid with strict limits on power, center frequency, 1 dB bandwidth, roll-off rate, etc. Accordingly, service providers and regulatory authorities are challenged by the compounding problems of increased number and density of users, increased user usage, and increased bandwidth/datarate demands. Deployment, operation and maintenance of next generation wireless services therefore results in increasing demand for test, monitoring and “visibility” of the wireless physical layer without requiring the similar deployment of large number of expensive personnel and/or equipment to at best accomplish intermittent and often inadequate monitoring.
In addition to ensuring wireless connectivity, preventing wireless connectivity has also become an issue. A growing segment of large corporate and government departments for example require the enforcement of a no-wireless policy. A no-wireless policy may be intended to prevent for example the inadvertent or malicious acquisition of sensitive, proprietary, confidential or secret information or to prevent triggering of an undesired incident, e.g. triggering of a chemical release. Such policy enforcement is challenged by the breadth and complexity of wireless devices, which are evolving rapidly in terms of functionality, complexity and performance. Applications for spectrum monitoring also extend to other environments, for example the battlefield wherein equipping military personnel and/or equipment with the means to monitor and analyze their RF environment for communication activity, signal jammers and other threats is becoming a necessity in today's world of ubiquitous wireless devices, improvised explosive devices with remote triggers, etc.
Today, these varying regulatory, service provider, military, and corporate groups must either deploy bulky broadband spectrum analyzers that are expensive, not designed for remote interconnected deployment and centralized management, and not designed for real-time analysis of wireless signals or exploit compact hand-held spectrum/signal analyzers targeted to specific narrowband system requirement. Neither solution addresses the requirement for compact, low cost, wide bandwidth, real-time spectrum analyzers that can be deployed in volume across geographic regions, providing analysis of signals that in many instances are characterized by short duration, varying frequency through frequency hopping, arbitrary frequencies, intermittent operation, and which may arise in-band or out-of-band with the normal environment of other wireless signals operating according to multiple protocols, often with high density. Accordingly, such compact, low cost, wide bandwidth, real-time spectrum analyzers would include, but not be limited to, real-time distributed spectrum analysis, interference detection, no-wireless or selective-wireless policy enforcement, spectrum management, signals intelligence (SIGINT), communications intelligence (COMINT), electronic intelligence (ELINT) and signal/interference analysis.
Further, it would be evident that it would be beneficial for such a compact, low cost, wide bandwidth, real-time spectrum analyzers to provide both the option for high performance, wideband, fast, programmable wide frequency range operation and fast, high performance, narrowband, programmable predetermined narrow frequency range. As noted supra wireless-RF communications and other microwave applications range within the United States are covered by FCC regulations up to 300 GHz across a wide range of applications and systems (see http://www.ntia.doc.gov/osmhome/allochrt.html for allocations) whilst at the same time tens of millions of mobile consumer devices are operating within approximately 120 channels within a 25 MHz region. Accordingly, although within this document for discussion purposes, and by way of illustration, a RF receiver supporting these conflicting requirements with a frequency range from 0.0001 GHz (100 kHz) to 18 GHz is presented it would be evident to one skilled in the art that other frequency ranges may be addressed without departing from the scope of the invention.
Within the prior art high performance, wideband, fast, programmable wide frequency range operation for spectrum analysis has been supported by large RF test equipment, from companies such as Agilent, Tektronix, Anritsu, Ando, etc. typically costing $10,000 at the low end to $35,000 or more at the upper end. Such instruments exploit scanning RF receivers based upon super-heterodyne (SUPHET) techniques that are well known in the prior art wherein the received RF signal (RF) is mixed with a local oscillator (LO), i.e. heterodyned, converted to an intermediate frequency (IF) and processed.
In contrast fast, narrowband, programmable predetermined narrow frequency range spectrum analysis has been supported by smaller handheld test equipment from companies such as Fluke, Berkeley, and Agilent for example. Such instruments exploit direct-conversion receivers (DCR) as known within the prior art that are much simpler to implement in integrated circuit form than SUPHET receivers. In DCR the RF band of interest is translated down to the baseband in only one conversion and whilst shortcomings including DC and I/Q offsets within the baseband output arise in wide bandwidth applications these disadvantages are limited within constant frequency type applications such as found in high volume consumer device communications such as Bluetooth (IEEE 802.15), LTE, and Wi-Fi (IEEE 802.11). DCR is also known as a homodyne receiver. Further, such applications typically require pre-determined signal analysis or operate without spectral analysis at all. For example the Fluke AirCheck™ Wi-Fi Tester for IEEE 802.11a/b/g/n networks provides signal monitoring across Channels 1-14 in the 2.4 GHz band (2412-2484 MHz) but only Channels 34, 36, 38, 40, 42, 44, 46, 48, 52, 56, 60, 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140, 149, 153, 157, 161, 165 in the 5 GHz Band (5170-5320 MHz, 5500-5700 MHz, and 5745-5825 MHz). However, it is compact, lightweight, and only costs $2,000.
Accordingly, it would be beneficial for a single wideband receiver within a spectrum analysis instrument to support the DCR approach for high performance, wideband, fast, programmable frequency range spectral analysis and the SUPHET approach for fast, narrowband, programmable spectral analysis. The inventors according to embodiments of the invention have established a receiver design methodology wherein a single common RF circuit provides SUPHET receiver functionality wherein a single mixer is active within a predetermined portion of the common RF circuit and DCR receiver functionality when both mixers are active within the predetermined portion of the common RF circuit.
In common with most signal processing electronics there are competing tradeoffs between instantaneous bandwidth (IBW), real-time processing and operating frequency range (for example 0.0001-18 GHz) as well as all of these against cost. Typically within a Real Time Spectrum Analyser (RTSA) the operating frequency range primarily determined by factors such as RF amplifier design, filter design and semiconductor technologies whilst the processing speed and IBW are determined through a combination of the RF front-end, analog-to-digital converters (ADCs), digital processing (such as Fast Fourier Transform (FFT) for example), etc. Hence, trading off these competing performance goals and cost is impacted by both analog and digital portions of the RTSA. Traditional SUPHET spectrum analysers are implemented within the prior art by using custom application specific integrated circuits (ASICs) for the analog portions and high speed field programmable gate arrays (FPGAs) for the digital portion. These ASICs and FPGAs typically being built utilizing the highest performance integrated circuit (IC) design and manufacturing processes available. Accordingly, a SUPHET RTSA is essentially built using different manufacturing processes and circuit designs to the transceiver circuits that broadcast the RF signals it is designed to monitor. This is very different from spectrum and protocol analysers addressing specific telecommunications standards that can typically leverage the same ASICs and other circuit elements of devices operating according to those standards, such as cellphones, smartphones, PDAs, etc.
High speed FPGAs and custom ASICs are expensive and in some instances difficult to utilize. In high volume consumer applications such as Wi-Fi (IEEE 802.11), WiMAX (IEEE 802.16) and Bluetooth the transmitter circuits and receiver circuits are typically implemented with silicon based digital IC designs and processes whereas the RTSA is optimized towards to both digital and analog aspects for high performance measurement applications wherein it is beneficial to leverage new IC design processes optimized to aspects such as faster computational processing, improved serial data links, etc. as well as RF circuit integration rather than accepting performance tradeoffs, whilst meeting a wireless specification, in order to provide monolithic integration and exploit lower cost IC processes.
Accordingly as discussed supra and below in respect of FIGS. 1B and 1C respectively prior art spectrum/signal analysis techniques have been distinctly separated between those addressing broadband analysis using swept oscillator mixing and those addressing narrowband analysis within narrow frequency ranges established by wireless standards, typically via DCR. An alternative prior art approach, described below in respect of FIGS. 3 and 4 by the inventors, see N. Adnani et al in US Patent Application 2013/0,064,328 entitled “Radio Frequency Receiver System for Wideband Signal Processing,” exploits a RF receiver operated as a DCR over a limited frequency range and in order to process signals outside of the range of this DCR, these other signals were processed by either downconverter or upconverter circuits to bring the signal into the range where it could be processed by the DCR. However, whilst this receiver allows for wideband operation across the entire operating frequency range, it relies upon an IQ demodulator for conversion of the signal directly to baseband (zero IF). However, this IQ demodulator, subsequent baseband operational amplifiers and the dual-ADCs digitizing the I and Q signals require DC and IQ offset compensation. Such compensations are difficult to determine and apply in real-time such that methods of generating/applying offset correction would introduce latency into the signal processing chain which in turn would impact signal streaming rates and consequently demodulation bandwidth. Accordingly, whilst providing fast wideband scans and signal detection such a RF receiver is not suitable in other situations requiring wideband signal demodulation.
Accordingly, it would be beneficial for RF receivers with such spectrum analysis/signal analysis applications to overcome these limitations with a true hybrid architecture wherein a DCR may be used to scan a frequency band or a subset of a frequency band, e.g. from 3 GHz to 10 GHz. However, where a signal is detected, say at 4.5 GHz having bandwidth of 20 MHz, then the RF receiver can switch to SUPHET mode in order to enable processing of RF signals up to half the bandwidth of the DCR. Beneficially such SUPHET processing in this mode may therefore be performed without offset correction and therefore the latencies within the prior art RF receiver methodology removed or reduced.
Accordingly, it would be beneficial for embodiments of the invention implementing a dual SUPHET-DCR mode wideband receiver to similarly leverage high volume silicon based digital IC designs and processes where feasible and minimize requirements for higher cost ASICs and FPGAs. Accordingly, the dual SUPHET-DCR mode wideband receiver can satisfy the conflicting requirements of low-cost, high speed, wide IBW, large operating frequency range, and high sensitivity with field-deployable network interfaced modules. Accordingly, based upon embodiments of the invention, the inventors have established a dual SUPHET-DCR mode wideband receiver based RTSA allowing distributed analysis wherein determination of policy breaches, network performance, regulatory compliance, etc. are locally determined and exploited directly in network management or communicated to the central server and network administrators for subsequent action. Beneficially the RTSA according to embodiments of the invention provides for a scalable architecture wherein multiple RTSA modules may be synchronized providing enhanced spectral bandwidth, processing speed, and monitoring.
However, it would be apparent that such a hybrid receiver providing low-cost, high speed, wide IBW, large operating frequency range, and high sensitivity would have a wide range of applications including, but not limited to, spectrum analysers, protocol receivers, frequency agile receivers and transponders, network management, and EMC testing. It would further be evident that the deployment context of devices employing such hybrid receivers may include, but not be limited to, laboratory environments, remote stand-alone deployments, integration or deployment with other network infrastructure, hand-held or field-test deployments, as well as part of other civilian, Governmental and military systems and platforms.